1. Field of the Invention
The present invention relates to an optical writing device and an image forming apparatus including the optical writing device that prevents scattered toner and powder dust from entering the optical writing device.
2. Discussion of the Related Art
An electrophotographic image forming apparatus includes an optical writing unit having optical members, such as a semiconductor laser and a polygon mirror. In the electrophotographic image forming apparatus, an electrostatic latent image is formed on an image carrier by emitting a laser light beam from the optical writing unit to a surface of the image carrier. The electrostatic latent image is developed with toner supplied from a developing device and is formed into a toner image. The toner image formed on the image carrier is transferred to a recording medium, and is then fixed onto the recording medium. Subsequently, the recording medium having a fixed toner image is discharged from the image forming apparatus.
In this image forming apparatus, when scattered toner and powder dust enter an outer case that accommodates an optical writing unit, the scattered toner and powder dust can adhere to the optical writing unit, thereby interrupting the emission of a laser light beam from the optical writing unit. As a result, image quality can be deteriorated.
If image quality is deteriorated due to scattered toner and powder dust adhered to the optical writing unit, the optical writing unit needs to be cleaned. In this condition, it can require a lot of time and efforts for cleaning.
Especially when an optical writing unit is disposed below an image forming device including an image carrier and a developing device in an image forming apparatus, scattered toner and powder dust can tend to enter an outer case that accommodates the optical writing unit.
To prevent scattered toner and powder dust from entering an optical writing unit, some conventional image forming apparatuses employ an airflow generating mechanism that generates a flow of air in a space formed between an image forming device and an optical writing unit. For example, Published Japanese Patent application No. 2001-138574 describes an image forming apparatus employing an airflow generating mechanism.
However, when scattered toner and powder dust are blown off by airflow, some scattered toner and powder dust can scatter toward an optical writing unit.
In some full-color image forming apparatuses, such as a printer, image carriers and developing devices are disposed above an optical writing device. In this configuration, toner and powder dust scattered from the image carriers and the developing devices can enter the optical writing device and accumulate at positions where laser light beams are emitted from the optical writing device. Accordingly, the accumulated toner and powder dust interrupt the emission of laser light beams toward the image carriers, thereby causing an occurrence of a white streak image.
Therefore, as discovered by the present inventors, it is desirable to provide an optical writing device and an image forming apparatus including the optical writing device that prevents scattered toner and powder dust from entering the optical writing device, and which prevents the deterioration of image quality caused by scattered toner and powder entered in the optical writing device.